SSD relay with Moteino ? (Fotek SSR-40DA)

[Lukapple]

Hi.
I've SSR relay "Fotek SSR-40DA" (specifications: http://www.fotek.com.hk/solid/SSR-1.htm).
What do I need to drive that relay with Moteino?

Can someone explain me what is "Min. ON / OFF Voltage", which is: ON > 2.4V , OFF < 1.0V
And what is "Trigger Current":7.5mA / 12V?

Thanks.

[KanyonKris]

It means the SSR will for sure turn on when the input voltage is 2.4V or more, and it will for sure turn off when the input voltage is 1.0V or less.

The trigger current means the SRR requires at least 7.5mA to turn on at 12V. It may require more current at lower voltages.

Since the Moteino outputs 3.3V on it's IO pins, and each pin is capable of supplying 30mA, it will work fine for turning on this SSR.

Be aware that the total current of all turned on Moteino pins should not be more than 200mA. If you plan to use several SSRs, you should measure how much current it takes for the Moteino to turn  on just one to determine how many SRRs you can connect. For example, if it takes 20mA to drive one SSR, you should not connect more than 10 SSRs to the Moteino.

[Lukapple]

Ok great, so I can connect it directly to Moteino IO pins (without any additional diode and transistor  - like on EMR).
I will drive max 2 SSR per Moteino.
Thanks a lot for your answer.

[Felix]

One additional note about SSRs - they might not be the best choice in all cases. Resistive loads mwill work fine, but some inductive or capacitive loads may not like it. Some CFLs for instance will flicker or not work at all, etc...
Also they may require large heatsinks.

[Lukapple]

What do you suggest for switching on/off water boiler heater (220V, 2kW heater)? Will that SSR do the job?

[Felix]

That's a resistive load so it should work.

[ColinR]

I use an SSR for my beer fridge, amongst other things. This was done using the same relay you're using:

http://www.cupidcontrols.com/2014/10/cupid-remote-rf-enabled-temperature-controller/

There aren't (yet) pictures of the relay box it's controlling, but it's one of these:

http://www.cupidcontrols.com/2014/03/cupid-powered-output/

In the box, I put a transistor between the controller output and the relay contact. It somewhat isolates the controller output from the relay input, in that the coil (relay input) is powered by a voltage supply and the transistor does low-side switching, with the micro or Pi controlling the gate. I found that with these cheap relays, it's better to give it 5V than 3.3V. This also makes powering something that requires a higher voltage on the coil no problem, and the current supply to the coil is not limited by the micro or Pi.

Watch out, as these things are poorly and inconsistently made. Once I find a viable replacement, I'll move away from them. I've found entire batches incapable of switching certain loads.

C

[Felix]

Right, that's why I stay away from large SSD relays as well. I prefer the good old mechanical relays. "Infinite" isolation and no heating issues, drive them with a transistor... easy enough.
They are cheaper and safer than SSDs.

[Lukapple]

Nice project Colin.
Now you scared me, I'll probably switch to mechanical relay. Do you have any suggestions which one to use(min 20A)? Are there any already assembled kits available (with transistor, diodes,...)?

Thanks

[ColinR]

I don't think you should be scared of SSDs in general. Just the cheap chinese ones that aren't certified. In general, they are also more sensitive and prone to die from overvoltage and/or polarity issues. They also put off heat due to on resistance in the power FETs.

There is, however, a time and place for SSRs: when you need to switch fast and often. In scenarios where you are doing duty-cycling, mechanical relays do have a finite lifetime. You don't want to switch them every 500ms from now until eternity.

Good old mechanical relays are pretty damn bulletproof, and the mainstay of the industrial controls industry. Also cheap and small!

C

[ColinR]

Spend a little on an IDEC product:

http://www.newark.com/idec/rssdn-25a/ssr-din-panel-mount-660vac-32vdc/dp/80K6137

This is typically the line I use, but you won't find contact ratings above 15A or so, but for DIN rail-mounted stuff:

https://www.idec.com/language/english/catalog/Relays/RelaySocketFamily.pdf

Here is 12V coil 30A mechanical that you can get in PCB mount:

http://www.mouser.com/ProductDetail/Omron/G8P-1A2T-F-DC12/?qs=sQVrL4YZhsQyUvjPK9kyzg%3D%3D&kpid=2097992&gclid=CNark9yaqsECFQuOaQodlQEAow

I'm going to release a mote temperature controller soon, but the relay on it probably won't be more than 10A.

C

[Lukapple]

Thanks for info.
I've already ordered one Fotek SSR-40DA . I'll probably switch to mechanical relay. Relay will be triggered only 1-2 times/day (water boiler heater).

[Lukapple]

Does anyone have experiences with ULN2003A, which can be used for controlling relay?

[ColinR]

I have a couple of these laying around, but never used them because I could always get away with a 2N7000 or 2N3904.

Colin